1. Field of the Invention
The present invention relates to an electron gun in a color cathode ray tube or a high definition industrial monitor, and more particularly, to an electron gun in a color cathode ray tube which can form a large sized main focusing electrostatic lens.
2. Background of the Related Art
FIG. 1 illustrates a cross section of a related art color cathode ray tube.
Referring to FIG. 1, the related art color cathode ray tube is provided with a panel 1 having red, green, and blue fluorescent materials coated on an inside surface thereof, a funnel 2 fixed to a rear of the panel 1, an electron gun 5 in a neck part 3 of the funnel 2 for emitting electron beams 4 toward a screen, a deflection yoke 6 mounted around an outer circumferential surface of the neck part 3 for deflecting the electron beams 4 emitted from the electron gun 5 in up, down, left, right directions, and subjecting the electron beams to self convergence, and a shadow mask 7 provided close to the inside surface of the panel 1 for selective pass of the electron beams 4. The electron gun 5 has three independent cathodes 8 arranged on a horizontal line for emission of the electron beams, a control electrode 9, an acceleration electrode 10, a pre-focusing electrode 11, a first focusing electrode 12, a second focusing electrode 13 having horizontal electrodes 133b on upper and lower sides of electron beam through holes 133a; an anode 14, and a shield cup 15 for shielding a geomagnetism.
When the aforementioned cathode ray tube is put into operation, the electron beams are emitted from the cathode 8, and controlled, accelerated, and pre-focused as the electron beams pass through the control electrode 9, the acceleration electrode 10, and the pre-focusing electrode 11. Then, the electron beams are converged in a horizontal direction and diverged in a vertical direction by a dynamic quardrupole lens formed by a voltage difference of the first and second focusing lenses 12 and 13 and a horizontal lens 131b, focused mainly by a main focusing electrostatic lens formed by a voltage difference of the second focusing electrode 13 and the anode 14, and accelerated into an inside of the cathode ray tube by the anode. In continuation, the electron beams are deflected in up, down, left, right directions and subjected to self convergence on the same time by a deflection signal from the deflection yoke 6. While the deflection yoke 6 subjects the electron beams to self convergence, it has a drawback in that the electron beams are converged in up and down directions and diverged in left and right directions. However, as the electron beams are pre-corrected by the dynamic quardrupole lens, the electron beams 4 passed through the deflection yoke 6 are directed to the shadow mask 7 without any distortion, selectively pass through the shadow mask 7, land on a fluorescent surface 16 of the fluorescent materials, to form a picture. A quality of the picture formed thus can be made the better as a spot diameter of the electron beam landed on the fluorescent surface are made the smaller.
In general, the spot diameter of the electron beams on a screen is influenced from a magnification of a lens, a spatial charge repulsive force, a spherical aberration of the main focusing electrostatic lens, and the like. Since the influence of the lens magnification on the spot diameter Dx of the electron beams is defined by a basic voltage condition, a focus distance, a length of the electron gun, and the like, it is of little use, and has very little significance as a design parameter of the electron gun. The spatial charge repulsive force is a phenomenon in which the spot diameter of the electron beams are enlarged as the electrons in the electron beams repulse and collide to one another. Therefore, for reducing enlargement of the spot diameter Dst of the electron beams caused by the spatial charge repulsive force, it is favorable that a travelling angle of the electron beams(called xe2x80x9ca diverging anglexe2x80x9d) is designed to be great. Different from the spatial charge repulsive force, the spherical aberration of the main focusing electrostatic lens implies an enlarged spot diameter Dic of the electron beams caused by a difference of focus distances of electrons passed through a radical axis of the lens and electrons passed through a protaxis of the lens. Therefore, the smaller the diverging angle of the electron beams incident to the main focusing electrostatic lens, the smaller spot diameter of the electron beams can be obtained on the screen. In general, a spot diameter Dt of the electron beams on the screen can be expressed as the following equation.
Dt={square root over ((Dx+Dst)2+Dic2)}
Both the spatial charge repulsive force and the spherical aberration can be reduced by enlargement of a diameter of the main focusing electrostatic lens. That is, the enlargement of the main focusing electrostatic lens diameter can reduce the spatial charge repulsive force because the diverging angle is made great, and can also reduce the spherical aberration because the electron beams can pass a radical axis of the main focusing electrostatic lens.
FIG. 2 illustrates a graph showing a diameter of a main focusing electrostatic lens vs. a spot diameter.
Referring to FIG. 2, it can be known that the greater the diameter of the main focusing electrostatic lens, the less the enlargement of the spot diameter caused by the spherical aberration of the main focusing electrostatic lens, resulting to reduce the spot diameter of the electron beams on the screen. In general, a size of the diameter of the main focusing electrostatic lens is proportional to sizes of electron beam pass through holes formed in opposite surfaces of the second focusing electrode 13 and the anode 14. Therefore, for maximizing the diameter of the main focusing electrostatic lens, it is known that single electron beam pass through hole for passing of the three electron beams in common is formed in each of the opposite second focusing electrode 13 and the anode 14.
FIG. 3 illustrates a half section of a second focusing electrode 13 and an anode 14 for forming a large sized main focusing electrostatic lens in a related art electron gun, and FIG. 4 illustrates a perspective view of the second focusing electrode 13 and the anode 14 shown in FIG. 3 with a partial cut away view.
Referring to FIGS. 3 and 4, the second focusing electrode 13 is provided with a first cup formed electrode 131 having one end opened to the cathode 8, and the other end with a rim part 131b of a horizontally elongated track form as a unit therewith to form single electron beam pass through hole for passing the three electron beams in common, an electrostatic field electrode 132 having one side fixed to the one end of the first cup formed electrode 131 and three electron beam pass through holes 132a formed therein, and a second cup formed electrode 133 having one opened end fixed to the other side of the electrostatic field electrode 132, three electron beam pass through holes 133a, and horizontal electrodes 133b fitted to an upper portion and a lower portion of respective electron beam pass through holes 133a. The anode 14 is provided with a third cup formed electrode 141 having one end opened to the panel 1, and the other end opposite to the rim part 131b of the second focusing electrode 13 with a rim part 141b of a horizontally elongated track form as a unit therewith to form a thermal electron beam pass through hole 141a for passing of the three electron-beams in common, an electrostatic field electrode 142 having one side fixed to the one end of the third cup formed electrode 141 and three electron beam pass through holes 142a, a fourth cup formed electrode 143 having one opened end fixed to the other side of the electrostatic field electrode 142, and the other end with single electron beam pass through hole 143a for passing of the three electron beams in common, and a shield cup fixed to the other end of the fourth cup formed electrode 143. And, there is a flange part 132c or 142c on an upper portion and a lower portion of each of the electrostatic field electrodes 132 and 142 buried in and fixed to bead glass 17.
In the foregoing system, when the cathode ray tube is put into operation, there is a large sized main focusing lens formed in a space between the second focusing electrode 13 and the anode 14. However, the horizontally elongated electron beam pass through holes 131a and 141a leads the main focusing electrostatic lens to having a weak horizontal focusing power and a strong vertical focusing power. However, as the electrostatic field control electrodes 132 and 142 respectively fixed to the second focusing electrode 13 and the anode 14 serve to adjust the horizontal and vertical focusing powers for the electron beams identical, the electron beams passed through the main focusing electrostatic lens are focused the same in the horizontal and the vertical directions.
In the meantime, an original form of the system shown in FIGS. 3 and 4 has burring parts 131d and 141d as shown in FIG. 7A on inner circumferences of the rim parts 131b and 141b of the second focusing electrode 13 and the anode 14 extended toward the electrostatic field control electrodes 132 and 142, for reinforcing a weak deformation strength of the rim parts 131b and 141b. However, the burring parts 131d and 141d formed by pressing reduce horizontal and vertical diameters H and V of the electron beam pass through holes 131a and 141a in the rim parts 131b and 141b (called xe2x80x9crim part hole diameterxe2x80x9d). Therefore, as shown in FIG. 7B, in order to enlarge the rim part hole diameters H and V, the burring parts 131d and 141d in FIGS. 3 and 4 are removed, to use the second focusing electrode 13 and the anode 14 having the rim parts 131b and 141b only in the electron gun. However, even in the example of FIGS. 3 and 4, because a diameter of the neck part 3 is limited to 27 mm, and the rim parts 131b and 141b are formed by pressing, the rim part hole diameters are limited to 19.6 mm(H1) in the horizontal direction, and 9.2 mm(V1) in the vertical direction. And, since the removal of the burring parts 131d and 141d causes the rim parts 131b and 141b weaker to deformation, there is an error occurred in a symmetry between the rim part hole diameters H and V and the electron beam pass through holes 132a and 142a in the electrostatic field control electrodes 132 and 142, which causes a problem in focusing on the screen. The inevitable roughness of inside circumferential surface of the rim parts 131b and 141b due to the pressing causes discharge between the second focusing electrode 13 and the anode 14 by a voltage difference, which gives damages to the circuit and the cathode, and causes noises on the screen.
Accordingly, the present invention is directed to an electron gun in a color cathode ray tube that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an electron gun in a color cathode ray tube, which can prevent opposite rim parts on a focusing electrode and an anode and enlarge hole diameters in the rim parts for improving focusing onto the screen and prevents discharge between the focusing electrode and the anode.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the electron gun in a color cathode ray tube includes a triode including a plurality of cathodes for emission of electron beams, a control electrode for controlling amounts of emission of the electron beams, and an acceleration electrode for accelerating the electron beams, a pre-focusing electrode for pre-focusing the electron beams, an anode and a focusing electrode for forming a main lens for focusing the electron beams, rim parts each provided to opposite edges of the focusing electrode and the anode for passing of the three electron beams in common, and electrostatic field control electrodes each spaced away from respective rim parts, and provided to insides of the focusing electrode and the anode, wherein the focusing electrode includes a first cup formed electrode having one end opened to a screen, and the other end with electron beam pass through holes formed therein, and a second cup formed electrode fixed to the first cup formed electrode having one opened end, and the other end with electron beam pass through holes formed therein, the anode includes a third cup formed electrode having one end opened to the cathodes, and the other end with electron beam pass through holes formed therein, and a fourth cup formed electrode having one opened end fixed to the first cup formed electrode, and the other end with electron beam pass through holes formed therein, and the rim parts being separate first and second plate electrodes fitted to the opened ends of the first and third cup formed electrodes, respectively.
The electrostatic field control electrode to each of the focusing electrode and the anode is an abut portion of the other ends of the first and second cup formed electrodes and the other ends of the third and fourth cup formed electrodes, respectively. Each of the first and second plate electrodes includes a flange on each of upper and lower sides thereof buried in, and fixed to bead glass.
In another aspect of the present invention, the electrostatic field control electrode to the focusing electrode is a third plate electrode fitted between the other end of the first cup formed electrode and one end of the second cup formed electrode, and the electrostatic field control electrode to the anode is a fourth plate electrode fitted between the other end of the third cup formed electrode and the one end of the fourth cup formed electrode, wherein each of the third and fourth plate electrodes includes a flange on each of upper and lower sides thereof buried in, and fixed to bead glass.
In the another aspect of the present invention, flanges buried in, and fixed to bead glass are provided, not to the first and second plate electrodes, but to the third and fourth plate electrodes, for preventing the first and second plate electrodes from taking vertical pressures from the bead glass.
In the present invention, an outer side of an inside circumference of each of the first and second plate electrodes is tapered, for prevention of discharge occurrence, and the first and second plate electrodes have a thickness of 0.7-2.0 mm, thicker than the first and second cup formed electrodes for positive prevention of deformation of the first and second plate electrodes.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.